The present invention relates to a pulley that can be used with belt drive mechanisms.
The following two methods are used for disk rotation mechanisms of magnetic disk apparatuses that have conventional flexible magnetic disks mounted on them. One of these methods is the direct drive method where the turntable upon which the disk is mounted is directly driven by the drive motor. The other method is the belt drive method where a rotational drive force of the motor is transmitted to the turntable via a belt that is wound around the pulley fixed monolithically to the turntable.
The mechanism that transmits the rotational force to the turntable in the case of the belt drive method is configured of a drive side pulley that is fixed to an output shaft of the drive motor by pressing the pulley onto it, a driven side pulley fixed monolithically to the turntable, and a belt that is wound around both pulleys. Also, because a head carriage is provided between the turntable and the drive motor, a bending pulley provided between the turntable and the drive motor bends the belt so that it avoids the head carriage.
The pulley that is used in a conventional belt drive mechanism is formed into a cylindrical shape such as a pulley 1 shown in FIG. 1 , and has a section of a contact surface 1a taken along a center line of rotation, the surface being in direct contact with the belt. This section has a shape of straight line. A band-shaped belt 2 is wound on the contact surface 1a of the pulley.
In a pulley 3 that is used in another type of conventional belt drive mechanism, a V-shaped groove 3a is provided on an outer surface of the pulley 3 as shown in FIG. 2 , and an angled belt 4, a section of which as seen across the operating course has a square shape, is wound around the V-shaped groove 3a.
The pulleys 1 and 3 described above and used in conventional belt drive mechanisms are respectively supported so as to be freely rotatable, by a shaft 5 inserted into central holes of the pulleys. Conventionally, the shaft 5 is assembled so as to be perpendicular to a flat surface of a chassis of an apparatus main unit to which the belt drive mechanism is attached. However, an error in manufacturing accuracy or assembling accuracy of the chassis can cause the shaft 5 to be mounted at an angle to a perpendicular line.
In cases such as these, each of the pulleys 1,3 rotates in an inclined state but the contact surfaces of the pulleys 1,3 touched by belts 2, 4 (hereinafter termed simply "the contact surfaces") do not have a plane symmetrical shapes with respect to planes including a center lines of operating courses of the belts and thus the contact surfaces of the pulleys 1,3 cause the belts 2,4 to move in the direction of thrust. Because of this, the belts 2,4 transmit the rotation drive force to the driven side of the pulley while they move up and down in the direction of this thrust. Accordingly, in the pulleys that are used in the conventional belt drive mechanism, the inclination and rotation of the pulleys 1,3 in an inclined state causes the belts 2,4 to move up and down in the direction of the shaft so that there is a problem where the ration of the turntable, which is a driven portion, becomes unstable.
In addition, such unstable rotation of the turntable causes a problem of deterioration in the recording and reproduction performance of the magnetic disc apparatus which uses the rotation mechanism.